This invention relates to a magnetron provided with an external cavity to stabilize the frequency of operation of the magnetron, and particularly to a magnetron of the low voltage type which is capable of operating with D.C. operating potentials of less than 700 volts. Many such low voltage magnetrons are designed for operation with a power supply of the voltage doubler and rectifier type, which cannot be grounded.
Examples of prior art magnetrons with external cavities for frequency stabilization are disclosed, for example, in the U.S. Pat. No. 3,334,268, issued to E. T. Downing on Aug. 1, 1967, U.S. Pat. No. 3,334,267, issued to R. F. Plumridge on Aug. 1, 1967, and U.S. Pat. No. 2,517,731, issued to R. L. Sproull on Aug. 8, 1950. In all of these prior art devices, however, the external cavity resonator is galvanically connected to the magnetron tube. When the magnetron is utilized in a consumer appliance, such as an electronic oven, the oven into which the microwave energy is transmitted from the magnetron must be grounded for safety reasons, because of the high voltages experienced in the magnetron tube.
Even in the more modern low voltage magnetron tubes, such as those disclosed in U.S. Pat. No. 3,458,755 issued to James E. Staats on July 29, 1969, and U.S. Pat. No. 3,559,094 issued to James E. Staats on Jan. 26, 1971, both of which patents are assigned to the assignee of the present invention, where the operating potentials applied to the magnetron are in the range of about 222 volts to 700 volts D.C., the oven cavity must still be grounded. But low voltage magnetrons such as those disclosed in the Staats patents are designed to operate from a power supply of the voltage doubler and rectifier type, which, by its nature, cannot be grounded. Accordingly, external resonant cavities of the types disclosed in the prior art, which are galvanically connected to the magnetron tube, are not suitable for use with an ungrounded power supply and a grounded load.